The present invention relates to ceramic ware and, more particularly, is directed towards a method and apparatus involving the production of ceramic ware in a reducing atmosphere within an electrically heated kiln.
The process of producing ceramic ware involves the use of high temperatures. Kilns of various configurations have been used in the ceramic industry for firing of the ceramic ware, heat for such kilns being obtained from a variety of sources such as oil and gas combustion and electrical-resistance coils. The fuel fired kilns will, under the proper combustion conditions, naturally produce a reducing atmosphere in the kiln during the maturing process of ceramic ware production. The reducing atmosphere is, during some ceramic ware production steps, very advantageous.
The creation of a reducing atmosphere in an electrically heated kiln has met with limited success. Typically, the reducing atmosphere is introduced by burning small pieces of wood in the bottom of the kiln and the kiln is provided with an exhaust hole in the kiln top to allow exhaust gases and smoke and other particles to escape. In such kilns, however, the electrical-resistance heating elements, which are attacked by an active reduction atmosphere at temperatures about 2100.degree. F., are coated with a protective oxide crust by subjecting the elements to a high temperature in an oxidizing atmosphere. Flame produced particles, introduced into the kiln chamber for providing a reducing atmosphere, have resulted in premature failure of the electrical-resistance heating elements by removing, fusing into or penetrating the protective crust. The burning wood also often produces large quantities of undesirable smoke and soot.
The heating element decay problem is further compounded by the requirement that when the kiln must be operated at high temperatures, often above 2100.degree. F., active reduction must be continued to prevent reoxidation of the ware. This may further reduce the useful life of the heating elements.
One solution to this problem is the use of silicon carbide heating elements which are not susceptible to damage from a reduction atmosphere. However, while silicon carbide heating element type kilns do not have the element decay problem, they are much too costly for practical use by potters.
A principal object of the invention is therefore to provide an electrically heated kiln for ceramic ware production which does not suffer from the foregoing disadvantages.
Another object of the invention is to provide a method for producing a reducing atmosphere within an electrically heated kiln.
A further object of the invention is to provide a reliable, relatively low cost electrically heated kiln having the capability of providing a reducing atmosphere during the production of ceramic ware.